Image processing apparatus and method

ABSTRACT

An image processing apparatus which is capable of suppressing an increase in the circuit size of buffers between data-processing circuits, thereby enabling an associated component thereof to be implemented by hardware. A position control unit sequentially shifts a position of a sub window image by a predetermined skip amount in a predetermined scanning direction, for scanning, and further repeating the scanning for skipped sub window images, after shifting a start position of the scanning, to thereby determine positions of all sub window images each as an area from a face image is to be detected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus and animage processing method that detect a specific object from an inputimage.

2. Description of the Related Art

Methods for detecting a specific object from an input image include oneproposed by Viola and Jones (see P. Viola and M. Jones, “RobustReal-time Object Detection”, SECOND INTERNATIONAL WORKSHOP ONSTATISTICAL AND COMPUTATIONAL THEORIES OF VISION, Jul. 13, 2001).According to an algorithm that implements this method, a rectangularsmall area (hereinafter referred to as “a sub window”) is extracted froman input image, and it is determined whether or not a human face isincluded in the sub window. A description will be given of adetermination method with reference to FIG. 7.

FIGS. 7A to 7C are explanatory diagrams of a process for determining(detecting) a specific object (face-detecting process) by adetermination processing section of a conventional image processingapparatus.

A determination processing section 700 has a configuration in which aplurality of determination devices 70 (70-1 to 70-n) are cascaded, andeach determination device determines (detects) that there is a highpossibility that the image is a face, or that the image is not a face.The fact that a face is detected by the determination processing section700 means that it is determined by all of the determination devices thatthere is a high possibility that the image is a face.

For example, as shown in FIG. 7B, if a sub window 701 which contains aface in a small area thereof is input, the processing by thedetermination processing section 700 proceeds as indicated by a route702. The route 702 shows that it is determined by a first determinationdevice 70-1 that the sub window 701 is True (“True” indicates that it isdetermined that there is a high possibility that the image is a face).Then, it continues to be determined by all of the determination devicesfrom a next determination device 70-2 to a last determination device70-n that the sub window 701 is True, whereby it is determined that thesub window image 701 contains a face.

On the other hand, as shown in FIG. 7C, if a sub window 703 containingno face in a small area thereof is input, the processing by thedetermination processing section 700 proceeds as indicated by a route704. The route 704 shows that it is determined by the firstdetermination device 70-1 that the sub window 703 is False (“False”indicates that it is determined that the image is not a face). By thisdetermination, it is determined that the sub window 703 does not containany face.

The above-described process indicates that if it is determined by adetermination device in a preceding step that the image is not a face,processing to be executed by determination devices in following stepscan be omitted. Therefore, the number of steps to be executed forprocessing of a background part is reduced, which takes much load offthe image processing apparatus.

However, since the processing of a face part for the determination isperformed by all of the determination devices, the number of steps to beexecuted is large, which increases load on the devices. Further, also inthe vicinity of the face part, there is a tendency that it is determinedthat the image is not a face in one of the subsequent steps, which makesthe load heavier than that on the processing of the background part.

As an example of implementation of the above-described algorithm byhardware, there has been proposed a method of cascading data-processingcircuits that perform processes associated with one or a plurality ofdetermination devices. In this method, a buffer for data queue isprovided between each adjacent pair of data-processing circuits toprevent input from the preceding step to the following step from beinginterrupted.

It is envisaged that the size of the buffer is determined when designingthe determination processing section 700 such that a sufficientthroughput can be ensured even in a state in which the largest load isexpected, or such that demanded processing time is ensured.

FIG. 8 is a flowchart of a sub window position control process executedby the conventional image processing apparatus.

A description will be given of a conventional sub window positioncontrol method for determining a position of a sub window extracted froman input image with reference to the flowchart in FIG. 8.

In a step S801, a vertical position of a sub window to be extracted isinitialized so as to set a start position of the sub window. In a nextstep S802, a horizontal position of the sub window is initialized so asto set the start position of the same. These steps form aninitialization phase.

FIG. 9 is an explanatory diagram showing the movement of the sub windowposition during the sub window position control process executed by theconventional image processing apparatus.

As an upper left coordinate position of a sub window 902 in an inputimage 901 to be extracted, a horizontal position of the upper leftcoordinate position is denoted by Ph, and a vertical position of thesame is denoted by Pv, which are respectively initialized to 0. Theposition of the sub window 902 in the input image 901 shown in FIG. 9 isthe initial position of the sub window.

Next, in a step S803, Ph and Pv are respectively assigned to an outputhorizontal position Outh and an output vertical position Outv, asoutputs of the position of the sub window 902 acquired from the inputimage 901.

Next, in a step S804, the horizontal position Ph is incremented by 1 toupdate the same so as to move the sub window by one pixel in thehorizontal direction. The sub window moved from the position of the subwindow 902 by one pixel in the horizontal direction is a sub window 903.

Next, in a step S805, it is determined whether or not the sub window hasreached a horizontal end position. In the case of the position of thesub window 902, the answer to the question of the step S803 is NO, sothat the process returns to the step S803 to repeat the above-describedprocessing, whereby the sub window is sequentially moved to sub windows903, 904, et seq. in the horizontal direction.

The sub window is thus sequentially moved in the horizontal direction,and finally the position of a sub window 905 as the horizontal endposition is reached. This makes the answer to the question of the stepS805 affirmative (YES), thereby terminating the loop of the processingin the horizontal direction. In the following step S806, to shift thesub window by one pixel in the vertical direction, the vertical positionPv is incremented by 1 to update the same.

Next, in a step S807, it is determined whether or not the sub window hasreached a vertical end position. Since the position of the sub window905 is not the vertical end position, the answer to this question is NO,so that the process returns to the step S802 to initialize thehorizontal position Ph, which causes the sub window to be placed in theposition of the sub window 906.

Thereafter, the movement processing is repeated in the horizontal andvertical directions. When the sub window reaches the position of a subwindow 907 at the vertical end position, the answer to the question ofthe step S807 becomes affirmative (YES), thereby terminating the loop.

Although this is the conventional scanning sequence, the scanningsequence illustrated in FIG. 8 is the same as that of so-called rasterscan.

However, the conventional algorithm with which a specific object isdetected from an input image has a feature of tendency that sub windowsin the vicinity of a specific object each continue to be determined tohave a high possibility that the image is of a specific object, up tosteps closer to the final step.

Therefore, according to the scanning sequence as illustrated in the subwindow position control process in FIG. 8, since the sub window ismoved, pixel by pixel, in the horizontal direction, as the sub window iscloser to a face to be detected, the processing is more liable toproceed to steps closer to the final step. As a result, heavy loadprocessing is continued, which increase load per unit time.

FIG. 10 is a timing diagram of a sub window image process executed bythe conventional image processing apparatus.

A description will be given of why the performance of the apparatus isdegraded when the heavy load processing is continued with reference tothe timing diagram in FIG. 10. In FIG. 10, the horizontal axisrepresents time, and the vertical axis represents sub window images andthe types of the images, which are sequentially input according to thescan order. Further, the order of arrangement of the sub window imageson the vertical axis from the top corresponds to the order of inputtingof them from the start.

First, it is assumed as a precondition that determination devices fordetermining whether or not the possibility that an input image is a faceis high are implemented by data-processing circuits (hereinafterreferred to as “the stages”). The stages are a stage 1 (S1 in FIG. 10)and a stage 2 (S2 in FIG. 10) which cascaded, and the stage 2 is assumedto require more processing time than the stage 1.

If a sub window image containing a face (face image) is transmitted tosuch a system, data-processing is performed by the stages 1 and 2 in thementioned order, and if a sub window image containing no face (non-faceimage) is transmitted to the system, the data-processing is performedonly by the stage 1. If face images 1 to 3 are continuously input, thisleads to a state in which the face images 2 and 3 are caused to waitbefore processing of a preceding face image is completed by the stage 2.

To enable images to wait for processing by the stage 2, it is requiredto provide buffers between the stages. However, in a case of processingon a sub window-basis, it is necessary to buffer the data for each subwindow, and this increases the amount of data to be buffered increased.As a consequence, the size of each buffer circuit becomes so large thatit is difficult to implement the determination processing section 700 byhardware.

SUMMARY OF THE INVENTION

The present invention provides an image processing apparatus which iscapable of suppressing an increase in the circuit size of buffersbetween data-processing circuits, thereby enabling an associatedcomponent thereof to be implemented by hardware.

In a first aspect of the present invention, there is provided an imageprocessing apparatus that detects a specific object from an image,comprising an acquisition unit configured to acquire, from an inputimage, a small-area image as an area from which the specific object isto be detected, a position control unit configured to control a positionfor acquiring the small-area image by said acquisition unit, adictionary storage unit configured to store a dictionary for use indetermining the specific object, and a determination unit configured todetermine whether or not the specific object is present in thesmall-area image, using the dictionary, wherein said position controlunit sequentially shifts the position for acquiring the small-area imageby a predetermined skip amount in a predetermined scanning direction,for scanning, and further repeating the scanning for skipped small-areaimages, after shifting a start position of the scanning, to therebydetermine positions of all small-area images each as the area from whichthe specific object is to be detected.

In a second aspect of the present invention, there is provided an imageprocessing method for detecting a specific object from an image,comprising sequentially determining a position for acquiring, from aninput image, a small-area image as an area from which the specificobject is to be detected, acquiring the small-area image from thedetermined position, and using a dictionary for determining the specificobject, to thereby determine whether or not the specific object ispresent in the small-area image, wherein said determining a position foracquiring the small-area image includes sequentially shifting theposition for acquiring the small-area image by a predetermined skipamount in a predetermined scanning direction, for scanning, and furtherrepeating the scanning for skipped small-area images, after shifting astart position of the scanning, to thereby determine positions of allsmall-area images each as the area from which the specific object is tobe detected.

According to the image processing apparatus of the present invention, itbecomes possible to suppress an increase in the circuit size of buffersbetween data-processing circuits, thereby enabling an associatedcomponent thereof to be implemented by hardware.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a face detection unit for detecting a faceas a specific object, in an image processing apparatus according to afirst embodiment of the present invention.

FIG. 2 is a flowchart of a sub window position control process executedby the image processing apparatus in FIG. 1.

FIG. 3 is an explanatory diagram showing movement of a sub windowposition, performed in the sub window position control process in FIG.2.

FIG. 4 is a timing diagram of a sub window image process executed by theimage processing apparatus in FIG. 1.

FIG. 5 is a block diagram of a face detection unit for detecting a faceas a specific object, in an image processing apparatus according to asecond embodiment of the present invention.

FIG. 6 is an explanatory diagram of a face detection process executed bythe image processing apparatus in FIG. 5.

FIGS. 7A to 7C are explanatory diagrams of a process for determining aspecific object executed by a determination processing section of aconventional image processing apparatus.

FIG. 8 is a flowchart of a sub window position control process executedby the conventional image processing apparatus.

FIG. 9 is an explanatory diagram showing movement of a sub windowposition during the sub window position control process executed by theconventional image processing apparatus.

FIG. 10 is a timing diagram of a sub window image process executed bythe conventional image processing apparatus.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will now be described in detail below withreference to the accompanying drawings showing embodiments thereof.

FIG. 1 is a block diagram of a face detection unit for detecting a faceas a specific object, in an image processing apparatus according to afirst embodiment of the present invention.

In FIG. 1, the face detection unit is comprised of an image storagesection 101, a small-area image acquisition section 102, a scanningposition control section 103, a determination result storage section104, a determination section 105, and a dictionary storage section 106.

Next, a description will be specifically given of the respective modulesof the face detection unit.

The image storage section 101 stores input images, and it is possible torandomly access each of pixels of an input image.

The scanning position control section 103 sequentially determines theposition of a sub window to be processed for determination.

The small-area image acquisition section 102 reads a sub window image(small-area image) in the position determined by the scanning positioncontrol section 103, and supplies the sub window image to thedetermination section 105.

The determination section 105 refers to dictionary data stored in thedictionary storage section 106, and determines whether or not there is aface in the sub window image. A result of the determination is stored inthe determination result storage section 104 together with sub windowposition information.

Further, the dictionary data used by the determination section 105 isstored in the dictionary storage section 106, and a coefficient requiredfor determination and a look-up table (LUT) data and the like are alsostored in the dictionary storage section 106.

Here, the scanning position control section 103 sequentially computesthe position of a sub window image using a predetermined skip amount ina predetermined scanning direction. Further, the scanning positioncontrol section 103 repeatedly carries out scanning of skipped subwindow images each time shifting the start point for scanning, tothereby control positions of all of the sub window images which aresubject to the detection of a face as the specific object.

FIG. 2 is a flowchart of a sub window position control process executedby the image processing apparatus in FIG. 1. FIG. 3 is an explanatorydiagram showing movement of the sub window position, performed in theflowchart in FIG. 2.

The present process is executed by the scanning position control section103 in FIG. 1. Whenever the sub window position is shifted by thisprocess, the small-area image acquisition section 102 acquires eachimage of a sub window in the shifted position, and outputs the same tothe determination section 105.

The scanning position control section 103 performs processing fordetermining the left upper coordinate position of a sub window in aninput image 301 in FIG. 3.

Referring to FIG. 2, first, in a step S201, the scanning positioncontrol section 103 initializes a vertical position Pv to 0 to set astart position of a sub window to be extracted.

Next, in a step S202, the scanning position control section 103 sets avariable, referred to as a horizontal position offset Offseth, to holdan offset amount in the horizontal direction, and initializes thevariable by 0.

Next, in a step S203, the scanning position control section 103initializes a horizontal position Ph by 0 to set the start position ofthe sub window to be extracted.

Next, in a step S204, the scanning position control section 103 computesthe position of the sub window, which is to be notified to thesmall-area image acquisition section 102. An output horizontal positionOuth to be notified is a value obtained by adding the horizontalposition offset Offseth to the horizontal position Ph, and an outputvertical position Outv is the vertical position Pv. The first outputposition is the position of a sub window 302.

Next, a step S205 is a process for moving the position in the horizontaldirection, and the scanning position control section 103 updates thehorizontal position Ph to the value obtained by adding a skip amountSkiph to the horizontal position Ph. The skip amount Skiph, for example,uses the number of pixels corresponding to the width of a possible faceimage. The position moved from the sub window 302 by processing in thestep S205 is the position of a sub window 303.

Next, in a step S206, the scanning position control section 103 checkswhether or not the sub window position is a horizontal end position. Thehorizontal end position is the position of a sub window 304. Theposition of the sub window 304 is a horizontal end position of a subwindow which can be extracted from the input image 301 by the skipamount Skiph and is closest to a horizontal end of the input image 301.

In the case of the position of the sub window 302, it is determined inthe step S206 that it is not the end position, so that the answer tothis question is negative (NO). Therefore, the process returns to thestep S204 to repeat the processing for moving the position of the subwindow, using the skip amount Skiph in the horizontal direction, untilthe position reaches the horizontal end position.

When the processing for moving the position in the horizontal directionproceeds to finally bring the position to that of the sub window 304,i.e. the horizontal end position, the answer to the question of the stepS206 becomes affirmative (YES), so that the inner loop of the processingin the horizontal direction is terminated.

Next, in a step S207, the scanning position control section 103 performsprocessing for adding 1 to the horizontal position offset Offseth to setan offset to the next scan position in the horizontal direction.

Next, in a step S208, the scanning position control section 103 checkswhether or not all the positions have been scanned for the horizontaldirection. In the present embodiment, the scanning position controlsection 103 causes the respective positions of sub windows to be eachdetermined after skipping over the skip amount Skiph, and causes allpositions of sub windows in the skipped portions to be determined usingthe horizontal position offset Offseth in the second and subsequentexecutions of scanning.

Therefore, in the step S208, it is only required to check whether or notthe horizontal position offset Offseth becomes equal to the value of theskip amount Skiph.

A first-time scan brings the sub window position to the position of thesub window 304, and hence it is determined in the step S208 that thereare skipped portions, so that the answer to the question of the stepS208 is negative (NO). Therefore, the process returns to the step S203to perform a second-time scan.

The second-time scan is started from the position of a sub window 305.The position of the sub window 305 is offset, i.e. shifted in thehorizontal direction by the horizontal position offset Offseth from thesub window 302 which is the start position of the first-time scan.

Then, the second-time scan sequentially proceeds to a sub window 305, asub window 306, and so on, each time skipping over the skip amountSkiph. By repeating the above-described scanning process three, four, ormore times, all positions are scanned for the horizontal direction.Then, when all the positions are scanned for the horizontal direction,the answer to the question of the step S208 becomes affirmative (YES),so that the outer loop of the processing in the horizontal direction isterminated.

Next, in a step S209, the position of a sub window is shifted by onepixel in the vertical direction. Specifically, the scanning positioncontrol section 103 causes the vertical position Pv to be incremented by1 to thereby update the vertical position Pv.

Next, in a step S210, the scanning position control section 103 checkswhether or not the sub window is moved to the position of a sub window307, i.e. a vertical end position of the sub window. If the sub windowis not moved to the vertical end position, the answer to this questionis negative (NO), so that the process returns to the step S202 toperform scanning all positions for the horizontal direction.

When the process returns to the step S202, the sub window is in aposition shifted from the sub window 302 by the Pv pixels in thevertical direction.

Thereafter, the processing for scanning all positions in a skippingfashion in the horizontal direction is advanced in a manner shifting inthe vertical direction. This processing is repeated until the positionof the sub window reaches the position of the sub window 307, i.e. theend position. When the position of the sub window reaches the sub window307, the answer to the question of the step S210 becomes affirmative(YES), so that the whole loop is terminated.

The position control shown in the present embodiment is performed bydetermining all horizontal positions in the same vertical position, andthen shifting the vertical position.

However, it is also possible to obtain the same advantageous effects bya method of scanning the image by determining, in a first-time scan,horizontal positions in a skipping manner, and whenever reaching ahorizontal end position, displacing a vertical position, and in secondand following scans, the positions determined in the first-time scan aresequentially shifted to thereby determine all the positions. Further, itis also possible to obtain the same advantageous effects by a method inwhich the concept of the conventional scanning sequence is inverted byswapping the horizontal positions and the vertical positions, to therebyperform scanning in the vertical direction.

That is, this method is identical to the above-described method of theposition control of the present embodiment in respect of the point thatthe image is repeatedly scanned in a skipping manner, therebydetermining all the positions of sub windows.

FIG. 4 is a timing diagram of a sub window image process executed by theimage processing apparatus in FIG. 1.

When the inputting order of the sub windows in the vicinity of thespecific object is dispersed in a time axis direction by theabove-described method, it becomes as illustrated in FIG. 4.

In the conventional scan order shown in FIG. 10, the face images 1, 2,and 3 are successive, and then, non-face images 4 to 9 are successive.However, by applying the scan order of the present invention, a non-faceimage is put between successive face images in the order of processing,which make it possible to reduce occurrence of waiting for completion ofprocessing before a position shift. In FIG. 4, since the non-face imagescorresponding to not shorter than processing time required by the stage2 are put between the face images, it is possible to completelyeliminate the occurrence of waiting for completion of processing beforea position shift.

Although in the present embodiment, the description has been given,assuming that the skip amount Skiph is fixed in advance, it is possibleto store appropriate skip amounts as parameters in the dictionarystorage section 106 together with dictionaries, and change the skipamount according to switching between the dictionaries.

In this case, the skip amount Skiph used by the scanning positioncontrol section 103 is set to a selected appropriate one of the skipamounts stored in the dictionaries, which makes it possible to performscanning in which the processing load is dispersed.

The necessity of appropriately switching between the skip amountsdepending on the dictionary will be given hereafter.

For example, an area of a face and an area in the vicinity of the faceare different between a case where a face is detected using a dictionaryfor a sub window of 10×10 pixels, and a case where a face is detected bya dictionary for a sub window of 20×20 pixels.

As a specific example, if a skip amount of 4 pixels is optimum for thesub window of 10×10 pixels, it is favorable to double the skip amount to8 pixels for the sub window of 20×20 pixels.

This is because if the amount of movement for the sub window of 10×10pixels is applied to the amount of movement for the sub window of 20×20pixels, a sub window of a face and a sub window in the vicinity of theface become successive, which causes load concentration.

FIG. 5 is a block diagram of a face detection unit for detecting a faceas a specific object, in an image processing apparatus according to asecond embodiment of the present invention.

As another method of determining a skip amount, a skip amountcalculation section 107 appearing in in FIG. 5 may be provided forcalculation of the skip amount.

Sub window sizes are stored in advance in the dictionary storage section106 in association with respective dictionaries, and the skip amountcalculation section 107 determines a skip amount by multiplying, by apredetermined coefficient, a sub window size associated with adictionary which is selected by switching between the dictionaries.

This calculation is not limited to the multiplication using thepredetermined coefficient, but it is only required to determine the skipamount from a sub window size by a predetermined calculation formula.The sub window size is sometimes required to be changed when an objectto be recognized is changed, and in this case, it is possible tocalculate an appropriate skip amount from the sub window size. Thismakes it possible to set the appropriate skip amount, so that itpossible to maintain dispersibility of heavy load processing.

Further, although in the present embodiment, the description has beengiven of the case where all sub window positions in the image aredetermined, and it is determined whether or not a face is included inthe image of a sub window in each sub window position, it often occursthat detection of a face is required to be performed only on skin colorportions. Therefore, only skin color portions are sometimes extracted bypreprocessing. In this case, the face detection processing is onlyrequired to be performed in the areas extracted by the preprocessing.

FIG. 6 is an explanatory diagram of a face detection process executed bythe image processing apparatus in FIG. 5.

For example, if skin color potions are extracted from an input image 601shown in FIG. 6 by preprocessing, the skin color portions become faceparts and portions of background and arms in skin color, as shown by anarea 602, and hence the detection process is performed on the area 602.By applying the present invention to the area 602 extracted by theaforementioned preprocessing to perform scanning such that thepreprocessed data is read out in a skipping manner, it is possible toobtain the same advantageous effects.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2008-259764 filed Oct. 6, 2008, which is hereby incorporated byreference herein in its entirety.

1. An image processing apparatus that detects a specific object from animage, the image processing apparatus comprising: a small-area imageacquisition section configured to acquire, from an input image,small-area images each as an area from which the specific object is tobe detected; a scanning position control section configured to control aposition for acquiring each of the small-area images acquired by saidsmall-area image acquisition section; a dictionary storage sectionconfigured to store a dictionary for use in determining the specificobject; and a determination section configured to determine whether ornot the specific object is present in each of the small-area images,using the dictionary, wherein said scanning position control section:sequentially designates a succeeding vertical position in the inputimage after a completion of scanning in a preceding horizontal linethrough a preceding vertical position; designates a horizontal positionin a present horizontal line by sequentially moving from a startingposition by a predetermined skip amount in the present horizontal lineto sequentially acquire the small area images; and repeats the scanningprocess in the same horizontal line starting with a new startingposition that is shifted from the previous starting position of thepreceding scanning process of the same horizontal line, and sequentiallymoves from the new starting position by the predetermined skip amount,until all of the small-area images in the same horizontal line areacquired.
 2. The image processing apparatus according to claim 1,wherein said dictionary storage section stores the predetermined skipamount used by said scanning position control section.
 3. The imageprocessing apparatus according to claim 1, further comprising: a skipamount calculation section configured to calculate the skip amount by apredetermined calculation formula from a size of one of the small-areaimages, wherein the skip amount obtained by said skip amount calculationsection is set as the skip amount used by said scanning position controlsection.
 4. An image processing method of detecting a specific objectfrom an image, the image processing method comprising the steps of:acquiring, from an input image, small-area image each as an area fromwhich the specific object is to be detected; controlling a position foracquiring each of the small-area images acquired in the acquiring step;storing a dictionary for use in determining the specific object in adictionary storage section; wherein the position controlling step:sequentially designates a succeeding vertical position in the inputimage after a completion of scanning in a preceding horizontal linethrough a preceding vertical position; designates a horizontal positionin a present horizontal line by sequentially moving from a startingposition by a predetermined skip amount in a the present horizontal lineto sequentially acquire the smaller area images; and repeats thescanning process in the same horizontal line starting with a newstarting position that is shifted from the previous starting position ofthe preceding scanning process of the same horizontal line, andsequentially moves from the new starting position by the predeterminedskip amount, until all of the small-area images in the same horizontalline are acquired.